This application claims priority to German Patent Application No. 100 44 885.2 filed Sept. 12, 2000, which application is herein expressly incorporated by reference.
The present invention relates to a device that fills or deflates a tire. The tire is fillable with air. The tire is on a wheel of a vehicle, especially a tractor.
In tractors, a change of the air pressure in a tire is critical. During operation In the field, a lower tire pressure along with lower soil compaction provides higher traction. Low tire pressure during high speed operation of the tractor does not ensure driving stability, for example, 40 km/h. In the technical magazine profi-magazine for agrartechnik, 10/1995 xe2x80x9cDer Luftdruck im Reifen: Keine Ursache, grosse Wirkungxe2x80x9d (xe2x80x9cThe air pressure in the tire small causes, large effectsxe2x80x9d) different control systems may be found. According to this article, the rotary transmitters are arranged on the inner side or the outer side of the wheel according to the axle type. In inexpensive systems, the air supply is achieved from the outside past the wheel to the rotary transmission leadthrough. In the arrangement with an intermediate flange between the wheel and the wheel flange, the attachment of the rotary transmission leadthrough is achieved via the wheel screws. This embodiment has its advantages. An advantage is that no pipes are exposed to the outside. However, the critical screw connection is stressed to a higher degree by the enlarged free bending length of the wheel screws.
U.S. Pat. No. 4,804,027 describes a device to fill and deflate a tire. The tire is fillable with air and is coupled with a wheel of a vehicle. The wheel is integrated into a wheel hub. The wheel hub supports the wheel flange. The wheel hub forms the external component and includes a channel. A connection is connectable to the channel, which leads to the tire. An inner member, which is kept stationary and is provided with a connection to a pressure supply, is supported on the hub. Two seals are fixed to the inner member and distanced from each other. The seals, together with a valve arrangement enclose an annular chamber. The valve is a spring loaded valve. The valve is opened when a predetermined pressure in the chamber is exceeded. The valve guides the air into the channel of the wheel hub. However, the valve is formed such that it only opens when the seals abut the corresponding radially outside bore face of the wheel hub. The seals are always pressed by the full pressure, which is present to fill the tire, against the corresponding mating faces of the wheel hub. This is disadvantageous at high relative speeds, since the high pressure leads to high friction. Accordingly, the high friction also leads to correspondingly high wear of the seals. A further disadvantage is that the hub and the inner member are supported independently from each other by further components. Accordingly. radial deviations affect the seals.
DE 0S 1 605 743 describes a device to control tire pressure in vehicles. Here, a rotary transmission leadthrough has an outer member and an inner member. The members are rotatable relative to each other and are sealed towards each other by contact seals. The members are constantly subjected to a relative movement.
A tire filling unit is described in DE 0S 1 907 082. This reference discloses that it is necessary for vehicles with relative high circumferential speeds to switch the rotary transmission leadthrough during normal operation. Accordingly, during non-operation of the tire filling unit, no pressure exists. However, it has been found that problems occur with respect to the sealing elements of the rotary connection. This problem is very obvious, when large diameters are present, as in the case of tractors.
Therefore, it is an object of the present invention to provide a device to fill or deflate a tire, which ensures secure sealing over a long lifetime.
This object is solved according to the invention by a device for filling or deflating tractor tires. The drive includes a first connecting port in the wheel rim of the wheel. A housing with a second connecting port, including a bore, connects to the first connecting port on the wheel.
An inner member is supported in the housing. The inner member and housing are both rotatable relative to each other. A third connecting port connects a pressure supply means. A controllable valve is connected to the second connecting port. An annular chamber is connected to the second connecting port and the third connecting port. The annular chamber is formed between the housing and the inner member.
Two seals laterally close the annular chamber. The seals are arranged between the housing and the inner member. The seals are fixed on one of the two components, namely the housing or the inner member. The seals contact, in a sealing way, the mating faces connected to the other component by pressurization of the annular chamber. The seals are formed rotationally symmetrically to a longitudinal axis. Each seal has an annular attachment portion with a first outer diameter. The first wall portion starts from the annular attachment portion. The first wall portion departs from the longitudinal axis to an apex. The apex has a second diameter and continues with a second wall portion. The second wall portion is axially distanced from the first wall portion and the attachment portion. The second wall portion extends towards the longitudinal axis and ends in an axially projecting sealing lip. The sealing lip is arranged on a third diameter. The third diameter is sized to abut the mating face. Thus, the following relationship exists: an annular face between the first diameter and the second diameter is larger than an annular face between the second diameter and the third diameter. Further, the seal is axially elastic.
In this embodiment, the seals only abut a mating face, when a pressure is present. Thus, for the other operational times, in which no filling is carried out, the friction between the seals and the corresponding mating faces is practically reduced to zero. Because wear is reduced, a high life time is achievable, even though large diameters are provided for the seals, as the arrangement is provided on the wheel.
Further, it Is advantageous that even with large diameters at any given time, only small sections are in contact which would produce wear. Thus, a device is achieved which has a long life time. Further, it is advantageous that the seals abut the mating surface with a force. This force results from the difference of the two annular faces multiplied with the pressure. Because of this the friction is essentially reduced. Thus, a tire can be filled during driving. The axial abutment of the seal on the mating faces enables the radial play between the housing and the inner member to have no effect on the function of the seals.
Preferably, the seals are connected to the inner member and the corresponding mating faces are arranged on the housing. One of the two mating faces may belong to a component. The component is sealingly connected to the housing: for example a lid.
Advantageously the arrangement is achieved such that the seal, with its sealing lip, contacts the mating surface free of pretensioning. Alternatively, the seal is arranged with a small gap relative to this mating surface in the unpressurized state. Furthermore, the annular chamber is connectable to the free atmosphere via a valve.
From the following detailed description, taken in conjunction with the drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.